I've found the fix. It's the same, simple fix as all other Windoze fixes: reinstall XP Pro! Seriously, I think those of us who had the problems had added the drives long after XP Pro was installed. Installing XP Pro from scratch with the drive(s) attached seems to include the necessary services (i.e. Removable Storage) for their operation.
So now WS2 sees both of my drives, an internal Quantum DLT4000 (with new firmware and drivers from Quantum) and an external Quantum DLT VS80, with a choice of which to use.
NTBackup, the built-in backup utility in XP Pro, is a good basic test of workability. If it can see the drive(s), the option "DLT" will appear in addition to "File" in the destination drop-box. Stupid program doesn't indicate which drive it will use, you'll have to note which drive shows activity. If you only have one, well you'll have no worries.
Note: Both Yosemite Technologies TapeWare and Quantum's DLT Sage could, and still do, see and talk to the drives. But after installing one of them (I suspect TapeWare) NTBackup could no longer see the drives. Luckily it pointed out the need to start the "Removable Storage" service, which somehow (!) had been disabled. After starting it, first setting it to automatic, NTBackup could again see the drives.
I hope this helps somebody. I haven't yet tried to export an ISO image to tape via WS2, perhaps later when I've recovered my strength after this latest ordeal...
Doug
